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Background
On an Exchange 2013-2016-2019 server you can run into the following error:

Cause
This issue occurs because the access check fails between the Client Access server and the Microsoft Office Store: https://officeclient.microsoft.com/config16?CV=15.1.2242.10&Client=WAC_Outlook&corr=25d232df-4496-4350-a677-ad4f86eeb4ae
Solution
If the server that’s running Exchange Server has an internet connection, check the proxy server to see whether the following URL is enabled for access: If the server does not have an internet connection, you can safely ignore this error message. Or, you can use the following method to reduce the probability of the error occurring in the future.
This error occurs because Exchange tries to download an XML file which fails, usually because the server has no internet access. The error can be prevented by having Exchange make this call through a proxy server, use the Set-ExchangeServer cmdlet to achieve this:
Or other method
Change the interval for the Office Store access checks
- Open the following Web.config files in the Exchange Server 2013 Client Access Server or Exchange Server 2016 Mailbox Server:
- %ExchangeInstallPath%ClientAccess\exchweb\ews\web.config
- %ExchangeInstallPath%ClientAccess\Owa\web.config
- In Microsoft Exchange Server 2016, you must also change the REST Web.config file: %ExchangeInstallPath%ClientAccess\rest\web.config
- C:\Program Files \Microsoft\Exchange Server \V15\ClientAccess\exchweb\ews\web.config
- C:\Program Files \Microsoft\Exchange Server \V15\ClientAccess\Owa\web.config
- C:\Program Files \Microsoft\Exchange Server \V15\ClientAccess\rest\web.config
- In each Web.config file, add the following line between the “<appSettings>” line and the </appSettings> line. <add key = “KillBitRefreshTimeInSeconds” value = “<seconds>” />
For example, the following line sets the interval for Office Store access checks to 86,400 seconds (1 day): <add key = “KillBitRefreshTimeInSeconds” value = “86400” /> - From the administrative tools, start Internet Information Services (IIS) Manager.
- Select Application Pools, right-click each of the following pools, and then click Recycle:
- MSExchangeServicesAppPool
- MSexchangeOWAAppPool
- MSExchangeRestAppPool
Good luck
Phương Nguyễn